Non-intrusive velocity measurement of millichannel flow by spontaneous Raman imaging

A non-intrusive measurement technique based on spontaneous Raman imaging was proposed for investigating microscale flow structures. It has the advantage that it does not require tracer particles or fluorescent dye to measure fluid velocity and scalar quantities. Raman scattering from ions in solution is substance specific and is observed as Raman spectra that contain peaks due to molecular species. The spontaneous Raman intensity from an electrolyte solution strongly depends on the electrolyte concentration. Thus, a bandpass filter attached to an EM-CCD camera detects only the strong Raman scattering at the selected Raman shift. The spontaneous Raman image obtained was converted to an electrolyte concentration distribution by using a calibration curve that expressed the relationship between the Raman intensity and the concentration. The flow velocity in a millichannel was calculated from the peak-value displacement of the time-series concentration distribution.